Most document scanners include transparent surfaces through which the cameras receive an optical image of a document. This is done by either reflecting light off the surface of the document or transmitting light through the document. In many cases these transparent surfaces, often referred to as imaging guides, are designed by the scanner manufacturer to be wear items, which are field replaceable by either the customer or field service engineer.
It is often desirable to add upgrades to equipment presently in the field. This is difficult, however, because configurations are crowded and difficult to change without major overhaul of equipment. It would be desirable to use parts which are currently replaceable for maintenance to add upgrades to the paper feed path in pre-installed equipment.